Anorexia nervosa (AN) is an eating disorder characterized by a morbid fear of weight gain and a perception of being overweight despite objective evidence of weight loss and malnutrition. It has been estimated that almost 0.9% of women will suffer from AN at some point in their lives, and most cases of AN arise during adolescence. Even with appropriate treatment, only about half of patients with AN will have a full recovery, 30% partial recovery, and 20% will progress to having a chronic illness. Earlier, more aggressive treatment with appropriate nutritional recovery during adolescence offers the best chance of a full recovery. Treatment of AN is complicated by the high rate of comorbid psychiatric diagnoses, the physical and cognitive effects of the attendant malnutrition, and the lack of effective pharmacologic interventions. Approximately 75% of patients with AN have a comorbid psychiatric illness, including depression, obsessive compulsive disorder, and anxiety. Anxiety disorders in particular share attributes with AN, including perfectionism, rigidity, compulsivity, and harm avoidance in addition to trait anxiety. Complicating treatment, the risk and severity of patients' anxiety is enhanced by a lower body mass index (BMI), and this low BMI is the likely reason why standard medication treatments for generalized anxiety, such as selective serotonin reuptake inhibitors are ineffective. In order to address these treatment challenges, we propose to study the tolerability, feasibility and efficacy of a non-pharmacologic interventions for anxiety in adolescents with AN: omega-3 polyunsaturated fatty acid (PUFA) supplementation.